This invention relates to methods and apparatus for controlling material flow. One application of the invention illustrated and described herein relates to a mass flow variable orifice for close volumetric control of particulate solids such as cereal, grains or other granular materials discharged from a solid particulate material blender from hoppered bin bottom. The invention, however, may be utilized in other applications and environments.
Volumetric control of grain and product rates in most milling installations heretofore has been accomplished by slide gates, mass compensating powerless feeders, or powered feeders. Slide gates are low in cost and, hence, tend to be the most widely used control devices; however, in most practical applications, slide gates do not offer acceptable accuracy and tend to choke readily. Powerless feeders offer greater accuracy, with increased cost, but present undesirable calibration and sanitation problems. Powered feeders offer still higher accuracy at correspondingly increased cost yet pose uneconomical reliability and service problems. Still other control devices utilizing gravimetric feeding and scaling techniques offer even higher accuracy at substantially greater cost.
Cost heretofore has been the predominate factor in the selection of volumetric grain control devices and, hence, slide gates find almost universal application in grain milling installations. In many practical applications, however, a slide gate provides unacceptable or uneconomical flow control because flow instabilities make it exceedingly difficult to maintain the slide gates at an optimum opening cross-sectional area. For these and other reasons, therefore, flow control commonly is accomplished manually on the basis of a visual inspection of the actual flow conditions downstream of the slide gate, or on the basis of material requirements of downstream milling apparatus. Consequently, the flow rate obtained tends to fluctuate as the slide gate is adjusted manually in an attempt to optimize flow conditions, or the slide gate is left open at a less than optimum cross-sectional area; therefore, the downstream milling apparatus must be operated on the basis of the mean or minimum flow fluctuations obtainable. This, of course, leads to uneconomical operation of the downstream milling apparatus with resultant uneconomical reduction in overall capacity of the milling installation.